Aerospace Corrosion Control Chapter 8

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Questions and Answers

Where should you look for more in-depth information on corrosion?

FAA Advisory Circular 43-4B Corrosion Control for Aircraft

What is the 43-4B?

An extensive handbook that deals with the sources of corrosion particular to aircraft structures.

How does corrosion appear on the surface of aluminum alloys and magnesium?

It appears as pitting and etching and is often combined with a gray or white powdery deposit.

What are the two general classifications of corrosion that cover most of the specific forms?

Electrochemical attack Signup and view all the answers

In corrosion, what does the metal change into?

A metallic compound such as an oxide, hydroxide, or sulfate. Signup and view all the answers

What are the two simultaneous changes involved in the corrosion process?

The metal that is attacked or oxidized suffers an anodic change; the corrosive agent is reduced and is undergoing cathodic change. Signup and view all the answers

What is Direct Chemical Attack?

Direct exposure of a bare surface to caustic liquid or gaseous agents. Signup and view all the answers

What are the most common agents causing direct chemical attacks?

Spilled battery acid, battery fumes, residual flux deposits, and trapped caustic cleaning solutions. Signup and view all the answers

What are the four conditions for Electrochemical Attack?

A metal subject to corrosion (anode), a dissimilar conductive material (cathode) with less tendency to corrode, presence of a continuous conductive liquid path (electrolyte), and electrical contact between the anode and cathode. Signup and view all the answers

What factors of the metal determine the form of corrosion?

The metal involved, size, shape, specific function, atmospheric conditions, and the corrosion producing agents present. Signup and view all the answers

What does surface corrosion appear as?

A general roughening, etching, pitting on the surface, frequently accompanied by a powdery deposit. Signup and view all the answers

What may result from dissimilar metal contact in the presence of a conductor?

Excessive pitting damage. Signup and view all the answers

Dissimilar metal is in what class of corrosion?

Electrochemical attack. Signup and view all the answers

Why is dissimilar metal corrosion serious?

Often times it is happening out of sight and can only be detected before structural failure by disassembly. Signup and view all the answers

What can the improper use of steel cleaning products cause?

It can force small pieces of steel into the metal being cleaned, causing corrosion and ruining the adjoining surface. Signup and view all the answers

What is Intergranular Corrosion?

An attack along the grain boundaries of an alloy, commonly resulting from a lack of uniformity in the alloy structure. Signup and view all the answers

Aluminum alloys and some steels are susceptible to what type of electrochemical corrosion?

Intergranular corrosion. Signup and view all the answers

What is Exfoliation Corrosion?

An advanced form of intergranular corrosion that shows itself by lifting the surface grains of a metal by the force of expanding corrosion products. Signup and view all the answers

What is Fretting Corrosion?

Happens when two mating surfaces, normally at rest, become subject to slight relative motion. Signup and view all the answers

What characterizes fretting corrosion?

Pitting of surfaces and generation of considerable quantities of finely divided debris. Signup and view all the answers

What are some preventive maintenance strategies for corrosion resistance?

Material improvement, surface treatments, insulation, and modern protective finishes. Signup and view all the answers

What specific functions are included in corrosion PM?

Adequate cleaning, thorough periodic lubrication, detailed inspection for corrosion, prompt treatment of corrosion, accurate record keeping. Signup and view all the answers

Study Notes

Corrosion Control and Cleaning in Aviation

Refer to FAA Advisory Circular 43-4B for comprehensive corrosion information related to aircraft.
43-4B is an extensive handbook specifically addressing corrosion sources affecting aircraft structures.

Appearance and Classification of Corrosion

Aluminum alloys and magnesium exhibit corrosion as pitting and etching, often accompanied by a gray or white powdery residue.
Corrosion primarily falls into two classifications: direct chemical attack and electrochemical attack.

Corrosion Process and Chemical Composition

Corrosion converts metal into metallic compounds like oxides, hydroxides, or sulfates.
The corrosion process involves:
- Anodic change where the metal is oxidized.
- Cathodic change where the corrosive agent is reduced.

Direct Chemical Attack

Occurs due to direct exposure of bare surfaces to caustic liquids or gases.
Common agents include spilled battery acid, battery fumes, residual flux deposits, and trapped caustic cleaning solutions.

Conditions for Electrochemical Attack

Four conditions must be present:
- A metal undergoing corrosion (anode).
- A dissimilar conductive material (cathode) that corrodes less easily.
- A continuous conductive liquid path (electrolyte).
- Electrical contact between anode and cathode, often via rivets, bolts, or corrosion.

Factors Affecting Corrosion Form

The specific form of corrosion is influenced by:
- The type of metal involved.
- Size and shape of the metal.
- Specific functional use.
- Atmospheric conditions.
- Present corrosion agents.

Types of Corrosion and Their Implications

Surface corrosion manifests as roughening, etching, and pitting, frequently with a powdery deposit.
Dissimilar metal contact with a conductor can cause severe pitting damage.
Dissimilar metal corrosion is classified as electrochemical attack and can remain undetected until structural failure occurs.

Cleaning Challenges and Corrosion Types

Improper use of steel cleaning products can introduce small steel particles that cause corrosion.
Intergranular corrosion affects grain boundaries in alloys and is caused by alloy structure inconsistencies.
Aluminum alloys and some steels are particularly vulnerable to intergranular corrosion.
Exfoliation corrosion is an advanced intergranular type that lifts surface metal grains due to expanding corrosion products.
Fretting corrosion occurs when two stationary surfaces experience slight relative movement, characterized by surface pitting and debris generation.

Preventive Maintenance and Best Practices

Preventive maintenance for corrosion resistance includes material improvements, surface treatments, insulation, and advanced protective finishes.
Key corrosion PM functions:
- Regular cleaning and lubrication.
- Detailed corrosion inspections and protective system checks.
- Prompt treatment of corrosion and paint touch-ups.
- Accurate record-keeping and reporting of deficiencies.
- Use of suitable materials, tools, publications, and properly trained personnel.
- Maintenance of basic finish systems and keeping drainage paths clear.
- Daily draining of fuel cell sumps and cleaning of exposed critical areas.
- Sealing aircraft against water during poor weather and ensuring ventilation on sunny days.
- Replacing damaged gaskets and sealants to thwart water intrusion and entrapment.

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Description

Test your knowledge on Chapter 8 of the corrosion control textbook, focusing on cleaning and corrosion specific to aircraft. This quiz covers key references like FAA Advisory Circular 43-4B and the types of corrosion affecting aluminum and magnesium. Prepare to enhance your understanding of corrosion management in aviation.